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General Asteroid Information

[Asteroids] are small [metallic], [rocky] lumps that [orbit] the [sun] but are not [large] enough to be considered [planet]s. Asteroids lack an [atmosphere].

The [majority] of asteroids live in the main [asteroid belt], a circular asteroid [racetrack] between [Mars] and [Jupiter] that is approximately two to four astronomical units ([AU]) from the [sun]. Most main belt asteroids have a [stable], slightly [elliptical] [orbit], usually taking between three and six years to [circle] the [sun].

The [theory] on the existence of [asteroids] is that had the [gravity|gravitational] pull of [Jupiter] not been so [strong], the asteroids within the asteroid belt would have formed one conglomerated [mass] and eventually into a [planet] with an [orbit] between [Mars] and [Jupiter]. It is estimated that the [collective] mass of all the asteroids is 930 miles (1,500 kilometers) in [diameter], under half the size of the [moon].

There are three major characterizations of asteroids, which are determined by [composition], [albedo], and similarity to [meteor]ic samples:

  • [C-type asteroid|C-type] - ([carbon]aceous)
  • [S-type asteroid|S-type] - ([silica]ceous)
  • [M-type asteroid|M-type] - ([metal]ic)

Near-Earth Asteroids

Asteroids which come within 1.3 [AU] of the [Sun] are considered near-[Earth] asteroids. It is assumed that these asteroids have been knocked [free] from the main belt due to asteroid [collision]s or the gravitational influence of the planet Jupiter, or are the [remnant]s of [short-period comet]s. The largest known near-Earth asteroid is Ganymed, with an approximate [diameter] of 25.5 miles (41 kilometers).

There are three main characterizations of near-Earth Asteroids, named for [famous] examples of each:

  • [Amor Asteroid|Amors] - 1221 Amor
  • [Apollo Asteroid|Apollos] - 1862 Apollo
  • [Aten Asteroid|Atens] - 2062 Aten

Interesting Stuff

Several asteroids are [confirm]ed to have [moon]s orbiting them, including Ida (which the spacecraft Galileo took photographs of in a [1993] fly-by -- the moon was named Dactyl), and Eugenia (which was confirmed by the [Canada]-[France]-[Hawaii] [Telescope] on Mauna Kea in [1999]). This discovery allows observers to make more [concise] estimates of [mass] because of the gravitational [relationship] between the primary asteroid and its [moon]. These new observations have shown that many asteroids are far less [dense] than previously thought.